The present invention relates generally to digital communication networks, and more specifically, to methods and systems for efficiently transporting Fibre Channel/FICON client data over a SONET/SDH network path.
SONET/SDH and optical fiber have emerged as significant technologies for building large scale, high speed, IP (Internet Protocol)-based networks. SONET, an acronym for Synchronous Optical Network, and SDH, an acronym for Synchronous Digital Hierarchy, are a set of related standards for synchronous data transmission over fiber optic networks. SONET/SDH is currently used in wide area networks (WAN) and metropolitan area networks (MAN). A SONET system consists of switches, multiplexers, and repeaters, all connected by fiber. The connection between a source and destination is called a path.
One network architecture for the network interconnection of computer devices is Fibre Channel, the core standard of which is described in ANSI (American National Standards Institute) X3.230-1994. Arising out of data storage requirements, Fibre Channel currently provides for bi-directional gigabits-per-second transport over Storage Area Networks (SANs) in Fibre Channel frames that consist of standardized sets of bits used to carry data over the network system. Fibre Channel links are limited to no more than 10 kilometers. Similar to Fibre Channel is FICON, a proprietary I/O channel which was developed by IBM for the data storage requirements for main frame computers.
New standards and protocols have emerged to combine the advantages of the SONET/SDH and Fibre Channel/FICON technologies. For example, it is sometimes desirable to link two SANs, which operate with Fibre Channel or FICON protocols, over a MAN (Metropolitan Area Network), or even a WAN (Wide Area Network), which typically operate under SONET or SDH standards. This extension of SANs from 100 kilometers to over several hundred, or even thousand, kilometers, is made by mapping Fibre Channel/FICON ports to a SONET/SDH path for transport across a SONET/SDH network. One way to perform this function is to encapsulate Fibre Channel/FICON client data frames into transparent Generic Framing Protocol (GFP-T) frames and then map the GFP-T frames into SONET/SDH frames for transport across the SONET/SDH network. In this manner two Fibre Channel/FICON ports can communicate with each other over a SONET/SDH network as though the intervening network links are part of a Fibre Channel/FICON network. The Fibre Channel/FICON ports remain “unaware” of the SONET/SDH transport path. For example, see U.S. patent application Ser. No. 10/390,813, entitled, “Method and System for Emulating a Fibre Channel Link Over a Sonet/SDH Path,” filed Mar. 18, 2003 and assigned to the present assignee.
For the effective movement of data across SAN networks, these network systems have two types of flow control: 1) end-to-end, and 2) buffer-to-buffer credit. In both types of flow control, two Fibre Channel/FICON ports report to each other how many frames is available at the reporting port's buffer to receive Fibre Channel/FICON frames from the other port. In end-to-end flow control, the source and destination ports are the two ports and the ports signal each other the reception of a transmitted frame by an ACK Link Control frame. In buffer-to-buffer credit, the two ports on opposite sides of a link are the two ports and the ports communicate the reception of a transmitted frame with an R_Rdy Primitive signal. But flow control remains within the SAN network and is based on counting Fibre Channel/FICON frames which can vary. Flow control may also be extended across SONET/SDH transport networks which connect frame-based protocol networks, such as Fibre Channel/FICON and gigabit Ethernet. See, for example, U.S. patent application Ser. No. 10/613,426, entitled, “Method and System For Efficient Flow Control For Client Data Frames Over GFP Across a SONET/SDH Transport Path,” filed Jul. 3, 2003 and assigned to the present assignee.
Nonetheless, for SAN extensions, i.e., interconnecting SANs by SONET/SDH transport networks, the SAN extension devices (the Fibre Channel/FICON ports communicating over a SONET/SDH network) usually provide a large amount of buffering in order to maintain a 100% throughput over very long distances. Because of the large number of buffers in the SAN extension devices, a great deal of latency can be created for the frames passing through the devices. It is possible that sometimes the latency introduced by extra buffering can be a significant portion of the total latency, even compared to the latency of the long distance communication.
The present invention addresses this problem of inappropriate buffering with buffer management which is dynamic and intelligently selective for the particular SAN extension.